1983 Flagstaff Nighttime Cloudiness Summary Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Yr (nights) Photometric 11 3 6 9 19 15 8 4 10 7 5 2 99 Monthly Average: 8.3 Partial 3 3 2 3 7 1 1 3 1 5 0 3 32 Monthly Average: 2.7 Spectroscopic 5 2 0 4 2 6 3 4 0 2 3 4 35 Monthly Average: 2.9 Cloudy 12 20 23 14 3 8 19 20 19 17 22 22 199 Monthly Average: 16.6 -------------------------------------------------------------------------------- Clear Hours 152 50 66 86 157 94 52 47 88 85 52 40 969 Monthly Average: 80.8 Clear+Dark Hours 112 39 53 35 102 53 41 10 71 33 43 31 623 Monthly Average: 51.9 Mean Consec 3.7 1.0 2.0 1.8 3.2 3.8 2.7 2.0 2.5 1.8 1.7 1.0 Monthly Average: 2.5 Max Consec 8 1 3 4 7 5 4 3 4 3 2 1 Monthly Average: 3.8 -------------------------------------------------------------------------------- Definitions: Photometric - cloudfree dusk-to-dawn. Partial - at least 3 consecutive cloudfree hours during the night. Spectroscopic - less than about 1 mag. extinction throughout the night. Cloudy - cloudy. Clear+Dark Hours = photometric hours with moon absent. Mean Consec = mean number of consecutive photometric nights during the month. Max Consec = maximum number of consecutive photometric nights during the month.